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SQL Server T-SQL User-Defined Function of the Week
Getting a RowCount Without doing a Table Scan
Volume 1 Number 5 December 16, 2002
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http://www.novicksoftware.com/UdfOfWeek/UDF_FAQ.htm
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If you don't require an exact answer, it isn't necessary use a
SELECT count(*) query on the rows in a table to get the row
count. SQL Server keeps the row count in sysindexes and it
can be retrieved there. The key is to select the correct
record from sysindexes.
Sysindexes is a system table that exists in every database.
SQL Server maintains at least one row in sysindexes for every
user table. A few of the most important columns are:
Column Data Type Description
-------- ---------- ----------------------------------------
id int ID of the table referred to by this row
indid int See the text that follows...
rowcnt bigint Number of rows in the index
The indid column tells us what part of the table structure this
row of sysindexes is referring to:
indid value Description
----------- ----------------------------------------------------
0 Table data when there is no clustered index
1 Refers to the clustered index
2 - 254 Non-clustered indexes
255 Text or Image data pages
A table will only have an entry in sysindexes with an indid value
of for 0 or 1, never both. That's the entry that we're
interested in because its rowcnt field gives is the number of
rows in the table. There's a query that shows the table, index
and indid from the pubs database:
/------------- Copy From Below this line ----------------------\
USE pubs
GO
SELECT so.[name] as [table name]
, CASE WHEN si.indid between 1 and 254
THEN si.[name] ELSE NULL END
AS [Index Name]
, si.indid
FROM sysindexes si
INNER JOIN sysobjects so
ON si.id = so.id
WHERE si.indid < 2
AND so.type = 'U' -- Only User Tables
AND so.[name] != 'dtproperties'
ORDER BY so.[name]
\------------ Stop copying above this line --------------------/
(Results)
table name Index Name indid
--------------- --------------------- ------
authors UPKCL_auidind 1
discounts NULL 0
employee employee_ind 1
jobs PK__jobs__117F9D94 1
pub_info UPKCL_pubinfo 1
publishers UPKCL_pubind 1
roysched NULL 0
sales UPKCL_sales 1
stores UPK_storeid 1
titleauthor UPKCL_taind 1
titles UPKCL_titleidind 1
As you can see from the results, most of the indexes are
clustered (indid=1) but a few tables such as discounts
don't have a clustered index (indid=0).
I started this newsletter with "If you don't need an exact
answer..." That's because there are times when rowcnt is
not the exact number of records in the table. This can
be corrected by updating statistics on the table with:
dbcc updateusage
go
Here's the CREATE FUNCTION script for udf_Tbl_RowCOUNT:
/------------- Copy From Below this line ----------------------\
CREATE FUNCTION dbo.udf_Tbl_RowCOUNT (
@sTableName sysname -- Table to retrieve Row Count
)
RETURNS INT -- Row count of the table, NULL if not found.
/*
* Returns the row count for a table by examining sysindexes.
* This function must be run in the same database as the table.
*
* Common Usage:
SELECT dbo.udf_Tbl_RowCOUNT ('')
* Test
PRINT 'Test 1 Bad table ' + CASE WHEN SELECT
dbo.udf_Tbl_RowCOUNT ('foobar') is NULL
THEN 'Worked' ELSE 'Error' END
* © Copyright 2002 Andrew Novick http://www.NovickSoftware.com
* You may use this function in any of your SQL Server databases
* including databases that you sell, so long as they contain
* other unrelated database objects. You may not publish this
* UDF either in print or electronically.
***************************************************************/
AS BEGIN
DECLARE @nRowCount INT -- the rows
DECLARE @nObjectID int -- Object ID
SET @nObjectID = OBJECT_ID(@sTableName)
-- Object might not be found
IF @nObjectID is null RETURN NULL
SELECT TOP 1 @nRowCount = rows
FROM sysindexes
WHERE id = @nObjectID AND indid < 2
RETURN @nRowCount
END
GO
GRANT EXECUTE ON [dbo].[udf_Tbl_RowCOUNT] TO PUBLIC
GO
\------------ Stop copying above this line --------------------/
Let's use it:
/------------- Copy From Below this line ----------------------\
use pubs -- assuming the UDF was created in pubs
go
SELECT [name]
, dbo.udf_Tbl_RowCOUNT ([name]) as [Row Count]
FROM sysobjects
WHERE type='U' and name != 'dtproperties'
ORDER BY [name]
GO
\------------ Stop copying above this line --------------------/
(Results)
name Row Count
---------------------------------------- -----------
authors 24
discounts 3
employee 43
jobs 14
pub_info 8
publishers 8
roysched 86
sales 21
stores 6
titleauthor 25
titles 18
+--------------------------------------------------------------+
Do you have a great UDF that you'd like to share? Or maybe you
have a T-SQL problem that you think could be solved by a UDF
but you don't know how? Send them to:
UDF@NovickSoftware.com
and they might be published in this newsletter. I try
and respond to every request that I get.
Thanks,
Andrew Novick
+--------------------------------------------------------------+
This newsletter is published by Novick Software
http://NovickSoftware.com
Copyright (c) 2002 Novick Software. All rights reserved.
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